This invention relates to a hollow casing formed of plastic material and a method for manufacturing such a casing. More particularly, the present invention relates to such a casing and method in which the casing is molded from a polycarbonate material with its wall having a continuous, sinusoidal, cross-sectional configuration.
Traditionally, casings manufactured for use in industrial applications such as, for example, containers for large storage batteries, have been formed of a thermoset or vulcanized material, such as hard rubber. While such composition normally has the desired chemical and load resistant properties required, it is quite heavy, is not flame resistant, and has poor impact resistance. Also, the costs of hard rubber have been gradually increasing until the use of plastics has lately become a possible alternative.
However, the use of plastics in forming casings or other similar structures is not without problems. For example, in the manufacture of relatively large casings, the use of polyethylenes has been proven unsatisfactory since they lack the proper strength properties to accommodate the high mechanical stresses that are often placed on the casing. Also, thermoplastic polyesters, while having adequate mechanical strength, are often susceptible to attack by chemicals and, in addition, are often too costly to be economically feasible.
Of course, it is possible to produce a laminated structure of two plastic materials, one for supplying the required mechanical strength and the other having a proper resistivity to attack by chemicals. However, it can be appreciated that the requirement for two plastic materials increases the costs of materials and labor, often to unacceptable levels.